The invention relates to a module for producing a force hysteresis during pivoting of a rotary element which is mounted rotatably in a housing and on which there is secured at least one spring element, of which the free end slides, via a friction element, on a stationary friction surface.
Such modules are used, for example, in so-called xe2x80x9cdrive-by-wirexe2x80x9d systems, to simulate the frictional forces which are known from the hitherto conventional cable-control mechanisms, and result in a force hysteresis when the rotatably mounted elements are pivoted, in order to maintain the familiar actuating characteristics for the operator.
In addition to very high-outlay solutions as are known, for example, from German Patent Application 197 37 289.9, of which the complicated mechanical construction is expensive to produce and susceptible to malfunctioning during operation, a module of the type mentioned in the introduction is known from German Patent Application 198 48 091. Such a module can be arranged in addition, in the case of an actuating element provided with a restoring spring, in order to produce the desired force hysteresis. This previously known solution thus always requires two separate springs for producing the hysteresis and the restoring force. The larger number of components and the resulting higher installation outlay render the production more expensive.
The object of the invention is to provide a module which is intended for producing a force hysteresis and makes it possible to restore the rotary element with low design outlay.
The object is achieved according to the invention by a module of the type described in the introduction, in the case of which, in all the angled positions of the rotary element relative to the housing, the reaction force of the spring element subjects the rotary element to a restoring moment about the rotary spindle.
The module according to the invention provides the advantage that the spring element, on the one hand, produces the necessary restoring moment about the rotary spindle and, on the other hand, brings about the force which is necessary for producing the frictional forces and causes the friction element to butt against the friction surface. In addition to the reduction in the number of parts, which allows more cost-effective production, there is also a reduction, in relation to the hitherto known modules for producing a force hysteresis, in the amount of space required by the solution according to the invention. The level of the restoring moment and its relationship with the frictional forces produced may be achieved by different degrees of prestressing of the spring element, different geometries and/or by changing the friction-element/friction-surface friction pairing. Of course, the frictional force is only of such a magnitude that it does not obstruct to any great extent the restoring movement of the torque under the restoring forces.
In the case of many applications, it is desired for the restoring moment and/or the force hysteresis to be varied in dependence on the relative angle-of-rotation position of the rotary element. This can easily be achieved, in the case of an advantageous embodiment of the invention, in that the friction surface is arranged such that it curves with a changing radius about the rotary spindle. Corresponding curvatures make it possible to achieve regressive and progressive characteristic curves of the restoring force with changing levels of hysteresis. In a particularly straightforward embodiment of the invention, the housing contour forms the friction surface.
A preferred embodiment of the invention provides that the friction element is guided in a linearly displaceable manner in a guide of the rotary element, the guide path being located on a straight line running at a certain distance from the rotary spindle.
The eccentric arrangement of the guide path means that the reaction force of the abutment force of the friction element on the friction surface results in a restoring moment about the rotary spindle. It is conceivable, in principle, for the friction element also to be guided in a curved guide, in which case the tangents to the guide path should not intersect the rotary spindle in any angled position of the rotary element. In all the angle-of-rotation positions, the guides of the friction elements thus ensure a precisely defined restoring moment and precise abutment of the friction element against the friction surface.
The friction element may be guided, for example, in that the friction element is seated in a guide bore in the rotary element, said guide bore being adapted to the cross section of the friction element. This results in particularly uniform and low-friction guidance of the friction element, which ensures a constant contact-pressure force of the friction element on the friction surface.
A further preferred embodiment of the invention provides that the friction element is guided in a rotationally fixed manner in the guide bore. The rotationally fixed guidance may be achieved, for example, by a nose which extends in a groove formed in the longitudinal direction of the guide. Oval or polygonal cross sections of the guide bore may likewise prevent rotation, but involve higher outlay to produce. The rotationally fixed guidance ensures constant abutment of the friction element against the friction surface, this counteracting excessive wear of the friction partners and allowing the frictional forces to remain constant to the greatest possible extent during operation.
A further preferred embodiment of the invention provides that the spring element is a helical spring which is subjected to compressive loading and is seated in the guide of the friction element.
In the case of cylindrical guide bores, in particular, a very straightforward construction of the module is achieved since the guide bore for the friction element may simultaneously form the means for receiving the spring element. The operation of installing such a module is also very straightforward.
Two spring elements are preferably provided for redundancy.
A redundant system ensures that, even if a spring element fails, there is still a sufficiently high restoring moment available in order to restore the rotary element into its rest position. This avoids the situation where, following the rupture of a spring, an actuating element which is coupled to the rotary element remains in an operating position, this possibly resulting in malfunctioning. An example of such an actuating element is the gas pedal of a motor vehicle, which gas pedal must, in all circumstances, be restored into the idling position since, otherwise, dangerous situations could arise from the engine continuing to run under load.
The gas pedal or some other actuating element may be fitted or integrally formed directly on the rotary element. In the case of large numbers, in particular, such a module constitutes a variant which can be produced particularly cost-effectively. However, it is likewise conceivable for the housing to be sealed and to have a projecting shaft to which an actuating element can be coupled. Such a variant may be freely combined with different actuating elements and in addition, by virtue of the closed housing, provides the advantage that it is not possible for any dirt penetrating from the outside to settle on the friction surfaces or on the contact paths of a sensor which may possibly be provided for sensing the angle-of-rotation position.
The friction element preferably has a stop which, in the event of excessive wear of the friction element, interacts with a housing-side stop projecting into the pivot path thereof. Such a stop prevents the situation where, following a relatively long period of operation and inadequate maintenance, the friction-element wear is so severe that the friction lining of the friction element is totally worn and this results in further damage, or that, on account of a spring which is relieved of stressing to an inadmissibly pronounced extent, the restoring moment acting on the rotary element decreases to such an extent that a satisfactory restoring operation is no longer reliably provided. The limitation provided by the stop ensures that the spring is supported directly on the stop and the necessary minimum restoring moment is ensured as a result. Since the force hysteresis is selected predominantly with comfort in mind, a drop in the hysteresis action is accepted for safety reasons in the case of wear, which is inadmissible per se. A stop may also be expedient when a force hysteresis is only desired in any case in a limited angle range. With a corresponding configuration of the friction surface, the spring element may be supported on the stop over a certain angle range, while, in a further angle range, there is abutment of the friction element on the friction surface under the load of the spring element.
The stops are preferably located in a position in relation to one another which during pivoting of the rotary element, in the abutment region, essentially avoids relative movement between the stop surfaces. This avoids frictional movements which could result in wear of the stop surfaces themselves.